1. Technical Field
The present invention relates to a radioactive waste solidification method, and more particularly to a radioactive waste solidification method suitable to processing of high-dose radioactive waste having a high radioactive level.
2. Background Art
Radioactive waste generated from a nuclear facility and the like are solidified with cement or glass and are then converted to a form suitable for storage, transportation, and burial processing. Solidification with cement of various types of solidification processing is a method in which radioactive waste is solidified with cement and water, so this method is inexpensive and is also advantageous in that processing is easily performed. When high level radioactive waste is solidified with cement in a solidifying vessel, however, moisture included in a cemented radioactive waste generated by the cement solidification is subjected to radiolysis, generating a hydrogen gas. This hydrogen gas may affect the cemented radioactive waste itself or a facility after burial processing (refer to Japanese Patent Laid-open No. 2007-132787).
Therefore, in a radioactive waste solidification method described in Japanese Patent Laid-open No. 2007-132787, radioactive waste, cement, and water are mixed in a drum which is a solidifying vessel to produce a cemented radioactive waste, and the cemented radioactive waste is dried to eliminate moisture from the cemented radioactive waste through heating or pressure reduction at a stage in which uniaxial compression strength is 1.5 MPa or more and is 75% or less of predicted strength.
In solidification with glass in which water is not used, so even if a radioactive waste is at a high radioactive level, there is no fear that a hydrogen gas is generated. As described in Japanese Patent Laid-open No. 2011-46996, however, solidification with glass involves processing at a high temperature, so that a large melting facility and the like are needed.
Japanese Patent Laid-Open No. 62(1987)-124499 describes a radioactive waste solidification method. In this radioactive waste solidification method, solid or liquid radioactive waste are mixed with glass with a low melting point (the melting point is 400° C. to 800° C.), and the resulting mixture of the waste and glass is subjected to molding and baking or is melted by being heated and a vitrified radioactive waste is produced.
Japanese Patent Laid-Open No. 62(1987)-165198 describes a hydrothermal solidification method for high-level radioactive waste. In this hydrothermal solidification method for high-level radioactive waste, high-level radioactive waste, glass, and quartz powder are mixed, and the resulting mixture is further mixed with water. This mixture is supplied into a canister. The mixture in the canister is heated to 300° C. due to decay heat of the high-level radioactive waste, producing a vitrified radioactive waste through a hydrothermal reaction. In this hydrothermal solidification method for high-level radioactive waste, the surfaces of glass and quartz powder are melted due to decay heat and high-level radioactive waste is bonded.